Automatic telephone system



' March 18,1930.

F. LUBBERGER ET AL 1,750,848

AUTOMATIC TELEPHONE SYSTEM Filed Nov. 26, 1926 4 Sheets-Sheet '1 FL 174": L";

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Patented Mar. 18 1930 UNITED STATES PATENT OFFICE 1 FRITZ LUBBEBGER, OF BERLIN-SCHMEARGENDORF, AND MAX LANG-ER,

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NEAR BERLIN, GERMANY, ASSIGNORS TO.SIEME1\TS & HALSKE AKTIENGESELL- ,SGHAFT WERNERWERK, OF SIEMEN SSTADT NEAR BERLIN, GERMANY AUTOMATIC TELETHONE SYSTEM Application In large telephone systems with automatic working comprising several exchanges diificulties occur when allthe junction lines outgoing in a certain traflic direction from the calling exchange are unavailable andit is necessary to deviate the connections to the wanted exchange over other junction routes.

For this purpose a number of junction lines could be rendered'available in the group of which the connections can be deviated, and the incoming end of these junction lines could be directly connected to junction lines going to the wanted exchange, which is not accessible to the calling exchange over a direct route. Such an arrangement renders it necessary to divide the group of junction lines, but it is known that this would have a bad effect on the traflic carrying capacity of the junction lines and thus on the etficiency of the installation. P

Considerable difficulties also occur when.

connections are deviated over the junction lines used for calls between the calling exchange and theexchange used as an intermediate exchange for the deviated connect-ions, because these junction lines terminate at switches of a group selecting stage located in the building up of the connection beyond the group selecting stage, which determines the trafiic direction and therefore selects the exchange.

'Arrangements arealready known whereby the junction lines, which are used for the traffic between two exchanges are also used for the deviated connections. For thispurpose in the exchanges, over which the deviated connections pass, is repeated the group selecting stage that determines'the traflic direction,

.and this entails the provision of special devices for positioning these switches,.because the calling'partyonly transmits the trains of impulses required for the normal connecting Now the object of the present invention is to enable connections to be deviated without reducing the efiiciency of the group of junction lines to the exchange used as an interme-- diate exchange for he deviated connections and without repeating the group selecting junction lines going to the exchange, over.

filed November 26, 1926, Serial No. 150,911, and in Germany January 5, 1926.

stage. According to the invention this is achieved by automatically connecting by means of hunting switches the junction lines,

seized for deviated connections, to the junc tion lines outgoing in the desired traific direction.

According to the invention the arrangement can be so devised that the junction lines, which are used for deviated connections, are provided with two differently numbered means of access, and the selection of one of these means of access determines whether it is to be used for a deviated call or a direct call. The incoming ends of these junction lines can be provided with two switches connected in parallel, namely a switch for making a numerical and then a non-numerical selection and another switch making only a non-numerical selection. Each of these switches so corresponds to a particular means of access to the junction line that when one means of access, is taken into use only the switchmaking a numerical and then a nonnumerical selection is started up for setting up a connection in this exchange and when the other means of access is taken into use only the non-numerical switch is started up for setting up a deviated connection;

However, the incoming end of the junction lines to be used for deviated connections can be provided with only one switch, which, ad-

cording to the particular means of access 7 used, is positioned either by a numerical se-.

lying idle, on the contrary by means of call seekers can be connected up to the incoming end of the junction line a switch that is to be used for the connection to be set up.

The drawings show by way of example several methods of carrying out the invention.

The Figure 1 shows the arrangement according to the invention applied to a telephone area having three exchanges VSt I,

- VSt II and VS]? III,

. one auxiliary lead common to all the differently numbered means of access to the junc tion line.

The Figure 5 shows the application of the invention to two'wire junction lines.

' The .Figure shows an arrangement, in which the incoming ends of the unction lines to be used for the devia d connection have access to several groups 0 call seekers and'a call seeker belongingto a particular group is started upaccording to the connectionto be set up.

. vided with a switch which is positioned either -nected to the exchange VSt II, the first I The Figure 8 shows an example, in" which the incoming end of the junction line is proby a numerical selection followed by a nonnumerical one or is positioned only by a nonnumerial selection.

The main features of the invention will now be described with reference to Figure 1. If the subscriber Tln-lcwishes to set up a connection with the subscriber T1113 ,con-

group selector I.'GW1 is positioned onto the contact group DKQ and an idle junction line VLl to the exchange VSt II is seized, at which the numerical switches -II.GW2 and LW2 are positioned.

lines between the exchanges VSt I and VSt II are marked engaged for some reason or other. Inordernevertheless to be able to set up connections between the subscribers of the exchange VSt I and'those of .the exchange VSt II, a connection between the terminals land 2 is removed at the intermediate distributing frame, and in place thereof the terminal 1 is connected with the terminals 3. By means of this switching operation, the junction lines 7 VL2, which are connected to the third contact group DK3. and go to the exchange VSt III, are also connected in parallel to the second contact group DK2 and the connection between this contact group and the line group :VL2 is provided with two switches II.GW3 and MW located in parallel in the example shown in the Figurel. When a call is to be made to a subscriber ofthe exchange VSt III and for this pugose the I.GW1 is set ontothe contact group K3, only the group selector II.GW3 is started up and positioned in the manner hereafter explained, while the hunting switch MW is not afiected by this call. On the other hand, when a call is to be set up and at that contact group, which has to a subsc riber of the exchange VSt II, the I switching operation efiected at the distributing frame, prevents a junction line goingdi-' rectly in the desired tl'aflic direction to be seized. after the first group selector -I.GW1 ositioned on the second contact has been group D and a junction VL2 going to the exchange VS; III is seized. "The connection is deviated over this junction line VL2 and the exchange VSt III. As the first group selector LGWl has been set on the contact goup DK2 instead of on the contact group K3, the hunting switch MW is startedup and it hunts for a junction line VL3 going to the exchange VSt jII. For this connection the parallelly located switch II.GW3 cannot be operated for the reasons explained here after. At the exchange VSt- II a second group selector 'II.GW l and a final selector LW VL the deviated connection over the exchange VSt III then extends over the following junction lines and connecting devices:

subscriber ,TlnlfVWl, I.GW1, VLZ, MW,

VL3, II.GW4, LW2, Tln3. I

In the Figure 1' is indicated an arrangement, in which the deviation of connections over another exchange is dependent on a switching operation performed by the exchange staff, who connect at a distributingframe the junction lines, which are to be used for the deviated connect-ions, in parthe junction lines marked engaged.

Now the Figure 2 shows an arrangement, in which the deviation of the connections is efi'ected automatically. Here likewise the contact group DK2 is provided for calls to the exchange VSt II, while over the contact Now it will be assumed that all junction group DK3 are set up connections to the ex- 2 change VStIII; The junction lines VL1 going to the exchange VSt II are connected to are positioned over the junction linethe first five contacts of the contact group DK2. When all these lines are marked engaged, the switch I.GW1 automatically reaches the succeeding contacts, to which are likewise connected thejunction lines that are connected to the first contacts of the contact roup DK3. Hence when the switch I.GW1

' oes not find an idle line in the group VL1,

it automatically seizes an idle junction line 1n.the group VL2 without the assistance of the exchange stafi', thus the connection is automatically deviated.

In Figure 3v is shown by way of example an arrangement in which the trunk lines VLQ, which are to be used for deviated connections, are provided with a separate auxiliary lead for each means of access.

When a call is to be set up to a subscriber of the exchange VSt III, the wipers 3', 4 and 5 of the switch I.GW1 are positioned on the contacts 6, 7 and 8 of the contact group DK3;

Thereby the following circuit is established:

earth, test relay P1, wiper 5, contact 8, lead V1120, contact 1402, relay C1, battery, earth. The relays P1 and C1 are operated. The relay P1 rat the contacts 12121 and 13291 switches through the speaking leads, while the relay C1 at contact 1501 disconnects the relay C2 and hatteryirom the lead VL20Z and thus marks engaged the junction line VL2 in the second contact'group DK2. This junction line cannot be seized over the contacts 9, 10 and 11 of the contact group DK2, because when a test wiper reaches the test contact 11 no test circuit is closed.

At the incoming end of the junction line VL2 the relay C1 in the exchange VSt III initiates in any desired manner the positioning of the switch ILGWV3, which is to be next positioned by number impulses from the calling party.

When the junction line is seized by the first group selector I.GW1 for a deviated connec tion over the contacts 9, 10 and 11 in the contact row DK2, the relay P1 is energized in series with the relay C2 at the incoming'end of the junction line. The relay P1 again connects through the speaking leads, while the relay C2 marks engaged the junction line in the third contact group DKB, because by opening the contact 1402 it disconnects the relay 'Cl from the lead VL20. But the relay C2 also opens 'its'contacts 1602 and 1702, thereby disconnecting the speaking leads VL2a and VL2b from the leads going to the wipers 18 and 19 of the second group selector II.GW3 and connecting its speaking leads over the contacts 2002 and 2102to the leads 22 and 23, which only go to the nonvnumerical switch MW.

At its contact 2402 the relay C2, closes the following circuit of the motor magnet D1 of the switch MW: earth, contacts2402, 25292, self interrupting contact 260Z1, motor magnet Dl, battery, earth. The switch MW is moved on step by step over its bank contacts and is arrested when it reaches an idle junction line VL3 going to the exchange VSt II (see Fig. 1), because the following test circuit is then established: earth, contact 2702, windings I and II of relay P2, wiper 28, contact 29,relay C3, battery, earth. The relay P2 at its contact 25122 opens the circuit of the motor magnet D1, it marks engaged the selected junction line VL3 by short circuiting its high resistance Winding I at contact 30702, and at the contacts 31p2and 32102 it switches through the leads 22 and 23 and with them the speaking leads VL2a and VL2b of the 'unction line VL2 to the wipers 33 and 34 of the switch MIV, hence the speaking leads are now connected over the contacts 35 and 36 to the speaking leads 37 and '38 of the junction line; i V

In the.Fi"'ure 4 is shown an-arrangment with the three wire junction lines YL2 They consist of the two speaking leads and asingle auxiliary lead VL20 for the two means of access. The Figure 4 only shows the amtiliary lead VL20.

The junction line VL2 having been seized During this connection it is impossible for the junction line to be seized over the second means of access (contact 44DK2) because when a hunting switch reaches the contact 44, its test relay does not receiveenough current to operate it.

On the other hand when the junction line is seized over the contact 44 in the contact group DK2, the test circuit still contains the high resistance winding of relay C4. Hence the current flowing over the lead VL20 is so weal; that in addition to the test relay P3 only the relay C5 can be operated and not the relay C6. The relay C5 now connects up the switch MIV and disconnects the switch ILCFWZ; in the same manner as the relay C2 in the arrangementshown in Fig, 3.

At the outgoing end of the lead VL20 the relay C4 opens its contact 4204 and so marks engaged in the contact group D113 also the seized junction line. i

The Figure 5 shows an example for twowire unction lines VL2.

It will first be assumed that a two wire junction line VL2 has been seized over the contact group DK3, which is the indication that a connection is to be set up with a subscriber of the exchange VSt III. After the wipers 50, 51 and 52 have been set on the-contacts 53, 54 and 55, the following test circuit is established: earth, relay P3, test wiper 52, contact 55. contact 5608, relay" C7, battery, earth. The relay C7 marks the seized junction lin'e engaged.- so that it cannot be seized by a switch over it opens the contact 9007 and so disconnects the relay C8 from the test contact91. Furthermore the relay C7 closes its contact 5907 andso switches through the lower-speaking the contact group DK2, as-

lead of the junction line VL2.- For the present no circuit changes are initiated at the incoming end of the junction line.

When th e calling party transmits impulses "g the A1 in the following lse contact at a pre not shown, -wiper 50,

junctionflfli ne VIJQ,

con act ea 60..

switch II.GW3, the in1- The contact 63-a1 repeats impulses to the lifting magnet H1 of the switch II.GW3:

net D2 being connected up prematurely. At the functioning of the first impulse,.the clos-;

'ing of the contact 69a1 e'nergized the relay C9 asfollows: earth, contacts 6901, 7061, relay C9,-res'istance 71, battery, earth. The relay C9 opens its contact 7209 and prevents the re lease magnet M1 being energized after the contact 7810 is closed when the first lifting stepis taken. Furthermore by opening the/contact 7409 the relay C9 disconnects the relay C10 from the lead' 67. The closing of the contacts 7509 and 7609 prepares-the circuit of the rotary magnet D2 and the test circuit.

The following locking circuit-for the relay C9 is closed after the first lifting step: earth, battery, resistance 71, relay C9, off-normal contact 8070,-earth. After the relay B1 has been energized, the relay C9 is short circuited over the contacts 69011 and 8161 each time the relay Al is energized, butjit cannot fall back,

I because it is rendered slow acting Whenits I the relay A1 is disconnected.

' Theconnection is completed in any desired Winding is short circuited and because the con tact 6901 isclosed only momentarily.

'At. the end of thertrain of impulses the relay B1 falls back owing to the steering circuit over the lead 67 being opened, and at its contacts 6861 the relay closes the circuit of the rotary magnet D2: earth, contacts 8270, 83194,

7509, 6861', 8401, rotary magnet D2, battery, earth. In known manner the switch II.GW3' is moved step by step over the contacts in the selected group. When anidle line is found, the following test circuit is established: earth, winding 1 of'relay P4, contact 7609, winding II of relay P4, wiper 77, contact 85, resistance 86, battery, earth. The relay P4 is operated; by opening its contact 83,124 it intenrupts the circuit of the rotary magnet D2, by closing its'contact 87,04; which has already been. earthed over the off-normal contact 8870, it marks the seized junction line engaged to other switches because it short circuits, the high resistance winding Furthermore the speaking leads are switched through at the contacts 89324 and 90194. while at contact62p4 manner by positioning the, succeeding switches. At' the end of'the conversation the positioned switch II.GW3 is released by disconnecting earth from' the l relay P3 in any desired manner, which is of no interest here.

The disconnection of earth now causes the re lease of the relays P3 and C7. Upon the release-,of the relay C7 the following circuit is closed for initiatin switch ILGW3: earth, attery, relay F, contacts 9208, 9307 ,lead 67, contact 94010, relay B1, contact 6670, earth. The relays F and B1 areoperated. By closing its contact 9461, the relay B1 connects the relay A1 to the lead 60, while the relay F, by closing its contact 95f, likewise connects earth to the the release of thelead 60; hence the following circuit is established for energizing the relay A1; earth, contact 95;, lead 60, contacts6l010, 9461', re istance 95, rela relays Al and 1 close their contacts 6901 and 8161. The relay C9 now can fall back.

It opens its contact 7 609' and closes its con-' tact 9609, thereby short circuiting the winding II of the relay P4. The relay P4 having been kept energized over this winding during the call, it now falls back; by opening the contact 87,124 it disconnects earth from the wiper 77 and at contact 97124 it closes the circuit of the release magnet M1, which has been prepared at contact 7209: earth, contacts 7 370, 97124, 7209, release magnet -M1, battery,- earth. Upon operating, the release magnet M1 returns the's'witch II.GW3 to its normal.

position. 7' 1 When the switch ILGW3 has returned to its normal position, the contact 66k is opened, thereby interrupting the circuit of the relays B1 and F. Both the relays fall back and open the contacts 94121 and 95/, thus they relay A1 is also de-energized. Thus have been returned to their normal position all the switching means of the switch ILGW3 as well as the relays locatedat the outgoing end of the junction line.

It will now be assumed thatthe shown junction line VL2 is seized over the contact group DK2. The following test circuit is established after the wipers 50, 51 and 52 have been, positioned on the contacts 100, 101 and -91: earth, relay P3, wiper 52, contacts 91,

A1, battery, earth. The

9007, relay C8, battery, earth. The relay' C8 closes its contact 10208, which is in parallel with the contact 9007, furthermore at its contact 10308 it connects up the relay C7. Before the relay C7 can operate and switch through the speaking lead and open the contact 9307, the following circuit for energizing the relay ClO at the incoming end of the junction line has been closed: earth, contacts 10408,

9307, lead 67, contacts 940107409, 10501, relay C10, battery, earth. By closing its contact- 106010 the relay C10 locks itself in a holding circuit over the resistance 107 independent of the lead 67. The other switching operations performed by the relay C10 will be explained later on.

When the relay.C,8 was energized at the outgoing end of the junction lineit marked ,the seized line engaged to switches over the contact group DK3, becahse' it opens the confrom the test-contact 55.

At the incoming end of the junction line VL2v the relay C is energized and opens at the incoming end of the junction line,

the contacts 61010-and 941010, thereby disconnecting the leads, which go to the wipers of the switch I'LGW3, from the speaking leads 60 and '67 of the junction line VL2, and it connects these leads overthe contacts 108010 and109010 to the leads 110 and 111, which operations cannot affect the switching means of the switch II.GW3.' The relay C10 at contact 112010 now closes the circuit of the motor magnet D3 of the switch MW: earth, battery, contacts 112010, 113125, self interrupting contact 114053, magnet D3, battery, earth. Furthermore the relay C10 at its contact 115010 has connected the test relay P5 to the. test wiper 1 16. When the wipers of the switchMW reach the. contacts of an idle junction line .VL3, the following circuit func-' tions: earth, windings I and II of relay P5, contact 115010, wiper 116, contact 117, resistance 118, battery, earth. The relay P5 is operated and arrests the switch MW by opening the contact 113175. The seized junction line is marked engaged, because the high resistance winding I is short circuited. Furthermore at the contacts 120175 and 121795 the speaking leads are switched through The connectionis completed 1n any des red manner At the end of the call is interrupted the circuit existing over the relays P3 and C8 in the exchange VS t I. Both the relays fall back. The opening of the contact 10308 also releases the relay C7,which upon its release initiates the release of the switch e.- cause the following circuit functions over the lead 67 earth, battery, relay F, contacts 9208 9307, lead 67 contact 109010, lead 111, relay-B2," earth. The relay B2 closes ltscontacts 12252 and 12362. The relay F closes its contact 95f-and so establishes the following.

circuit: earth, contact 95;, lead 60, contact 108010, lead 110, contact 12252, resistance earth. The relay A2 124, relay A2, battery,- closes its, contact 12502. Over the serially connected contacts 12352 and 12502 the relay C10 is now short circuited and it falls back; Thereupon. opened, thus interrupting the circuit over the relay P5. The latter falls, back. The opening of the contacts 109010 and 108010 cause the circuits over the relays A2, B2 and F to be interrupted. These three relays fall back. All the switching devices of the junction lineboth at the incoming as well as at the outgoing end-have now been returned to their normal position. f'

In the examples shown in thfiFlgilI: there are two switches connectedin'flpa VL2, namely a switch for making a numerito the switch MW. The other switching its contact 115010 is nal-1. at the incoming end of the junction linesw cal followed by a non-numerical selection and a second switch making only a non-numerical selection. Now the Figures 6 and '7 show exhas access to two groups of call seekers AS II and AS III. When the junction line VL2 is taken into use over the contact group DK3, a switching operation is performed over the junction line the call seeker AS III.- When such a call seeker has been positioned on the junction line VL2, the latter-is connected with a group selector II.GW3.

On the other hand when the junction line VL2 is taken into use over the contact group .DK2, the switching operation performed when the junction line is taken into use, causes the starting up of a call seeker AS II associated withan idle junction line VL3 and the switch now seeks the junction line VL2, taken into use.

The switching operation, which efiects the starting up of a call seeker in one of the two groups, also causes the junction line to be made ready for testing only in the contact field of the call seekers 'of the particular group, that is. to say for example in the call seeke'r group AS III or in the call seeker group AS II.

In Figure 7 is shown an arrangement, in which the wipers of the call seekers AS II are not directly connected to the junction line -VL3, but the connection between the exchanges VSt III and-VSt II is effected by a double non-numerical selection, because a call seeker AS II hunts for the seized junc-.

for an idle junction line VL3.

In a similar manner a group selector II.GW3 is not directly associatedwith the call seeker AS III, and the connection between a seized junction line VL2 and an idle group selector II.GW3 is likewise set up by a double non-numerical selection, which is effected by the call seeker AS III and an interrlrliediate switchVW III connected therewit The Figure 8 shows an arrangement, in which a switch is associated with the incoming end 'of each junction line VL2, this switch being positioned either by a numerical selection followed by a non-numerical selection or is positioned only by a non-numerical selection. For example a Strowger switch can be used, which is provided with a special eleventh level. In their normal position, the

when the rotary magnetinstead of the lift- VL2 for starting upg'wipers of this switch standin front oflthis;

eleventh level, which is located below the-first :level used for the numerical selection.- Henc.

the switch has been taken intouse, the wipers are at once rotated over this special level. I If, on the contrary, the lifting magnet be first connectediup, the switch will be operated in the known manner and the wipers will be raised. by the lifting magnet to alevel only accessible by a numerical selection, whereupon the wipers are positioned on a contact of the selected level by connecting up the rotary magnet.

The junction line L3 going to the ex change VStII areconneted to the special eleventh level, in front of which the switch wipers normally stand. Hence the rotary magnet'has to be connected up at once if the outgoing end of the junction line VL2, (which is not shown in Figure 8) be taken into use over the contact group DK2; while if the means of access connected to the contact group DK3 be used, the lifting magnet is first connected up for making a numerical selection and then the rotary magnet is connected up for making a non-numerical selection.

7 It will now be assumed that VL2 is a two wire junction line. Hence its outgoing end is similar to that shown in the Figure 5..

.When the junction line is taken into use over the contact group DK3, the switch. will be positioned in the same manner as; that decuitof the rotary magnet D4. The relay G11 at contact 136011 closes the circuit of the rotary magnet D4: earth, contacts 135012,

137206, 136011, 13863, 139a3, rotary magnet D4, battery, earth. Hence the Wipers of the switch,II.GW3. are at once moved over the contacts in the lowest (eleventh) level by the rotary magnet D4, and in known manner they hunt for an idle junction line VL3. The test circuit over the relay P6 has been prepared by the relay C11 at the contact 140011. At the end of the call the release of the switch is initiated as in Figure 5 by maintaining the relays A3 and B3 energized for some time.

- The relays A3 and B3 at their contacts 141a3 and 142123 short circuit the rela C11, and at their contacts 143(13 and 14463 t ey short circuit the relay C12. Both relays fall back, bc-.

cause their windings remain short circuited for some time, and the release of the switch II.GW3 is thus brought about.

What is claimed is:

1. In a multiofiice telephone system, three ofiices, trunks from the first oflice to the second oflice, trunks from the first ofiice to the third oflice, trunks from the second oflice to the third oflice, switching mechanism in the first ofiice operative for extending a connection over one of said trunks to-the third otfice, said switch mechanism further operative re-' sponsive to a busy condition of the trunks from the first to the third oflice to extend said connection to the second ofiice byway of one of said trunksinstead of to said third oflice, a non-numerical hunting switch in said second oflice, and means responsive to said last mentioned extension for automatically operating said switch to hunt for a trunk extending from the second oflice to the third office.

2. In a telephone system, a trunk terminating in one end in a numerical switch and a non-numerical hunting switch and at the other vend in two branches, a switching mechanism having access to said branches, means whereby said mechanism is operated to seizesaid trunk from one of said branches to extend a connection, means responsive to a busy condition whereby saidv mechanism is operated to seize said trunk from the other of said branches to extend a connection, and means dependent upon the branch seized for determining whether said numerical switch or said non-numerical hunting switch is to be used for further extending said connections.

3. In a telephone system, aI'trunk terminating in one end in a numerical switch and a nonsnumerical hunting switch and at the other end in two branches, a switching mechanism having access to said branches, said trunk comprising a pair of talking conductors common to said branches, a test contact for each of said branches at .said other end, means for operating said mechanism to seize said trunk over one of said branches to extend a connection, means responsive to a busy condition whereby said mechanism is operated to seize saidtrunk from the other of said branches to extend a connection, and means operated over the said test contact as sociated with the branch seized for determining whether said numerical switch or said non-numerlcalswltch 1s to be used for fur-' ther extending the connections.

4. In a telephone system, a trunk terminating in one end in a numerical switch and a non-numerical switch and in the other end in two branches, a switching mechanism having access to said branches, said trunk comprising only a pair of talking conductors common to, both said branches, means for operating said mechanism to seize said trunk over one of said branches to extend a connection,

means responsive to a busy'condition where.

by said mechanism is operated to sci-'zesaid trunk from the other of saidbranches to extend 'aconnection, and switching means oper-- branch takeninto use for conditioning said numerical swltch to be respons ve to subseative in different ways, accord-ing to the said quent impulses or for automatically operating said non-numerical switch to further extend the-connections.

5. In a telephone system, a trunk termibranches, and switching means operative responsive to said seizure for disconnecting said numerical switch from said trunk and for connecting said non-numerical switch to said trunk.

6. In a telephone system, a two conductor trunk terminating in an automatic switch, a first and a second relayin said switch, means for operating said switch to extend a connection, means whereby said first relay is energized over a circuit including one talking conductor of said trunk, means operative responsive to said energization for energizing said second relay over a circuit including the other talking conductor of said trunk, and means responsive to the energization of said second relay for releasing said-switch.

7. In a telephone system, a two conductor trunk terminating in an automatic switch, a release and a test relay in said switch, means for operating said switch over-said trunk to extend a connection, said relays being energized by the operation of said switch, means controlled over the two conductors of said trunk for short cir'cuiting said release relay thereby causing said relay to deenergize, contacts on said release relay closed responsive to said deenergization for short circuiting said test relay thereby causing said relay to deenergize, and means controlled by said release and test relays for causing said switch to release.

- 8. In a telephone system, a two conductor trunk terminating in a switch, means for op erating said switch over said trunk to extend a connection, a pair of line relays in said switch, means controlled over said trunk for operating first one and then the other of said line relays, a release and-a test relay in said switch, means controlled by the operation of said line relays for causing the operation of said release relay; means controlled by the operation of said release relay for causing the operation of said test'relay, a release magnet in said switch, and means controlled by the operation of said release and test relays for operating sai'd release magnet to release said switch.

9. In a multi-oflice telephone system wherein an automatic switch has access to alternative trunk routes for extending a connection to a third exchange and wherein the first route includes trunks comprising only two talking conductors directly connecting the first and third exchanges while the alternative route includes trunks comprising only two talking conductors connecting the first and second exchanges and the second and third exchanges, means for operating said switch to directly select either of said routes by seizing a trunk to the third exchange or by seizing a trunk to the second exchange without. seizing a trunk to the third exchange, and means in the second exchange automatically operated over said conductors in case the alternative route is taken into use for connecting the trunk in use extending from the first exchange to the second exchange with a trunk extending fromthe second exchange to the third exchange in order to complete the connection. I

10. In a multi-office telephone system wherein an automatic switch in the first ofiice has access to a group of trunk lines extending to a third ofliceand to a group of trunk lines extending to a second ofiice and wherein a group of trunk lines extend from the second oflice to the third oflice, means responsive to an encountered all trunk busy condition of the trunk lines extending from the first office to the third office for causing said switch to seize a trunk line extending to the second exchange, and automatic switching means comprising a non-numerical hunting switch 'in said second exchange responsive to said seizure for automatically extending the connection to the third exchange over a trunk line extending from the second to the third exchange.

11. In a multi-ofiice, telephon system wherein a. switching mechanism in-Qthe first office has access to a group of trunks comprising only two talking conductors extending to a third oflice for extending connections thereto and to a group of trunks comprising only two talking conductors extending to a second .ofiice when all the trunks extending to the third oflice are busy and wherein a group of trunks extend from the second to the third oflices, means for operating said mechanism to seize an idle trunk in either group to which it has access dependent upon their busy conditions in order to extend a connection to the third oflice, and a non-numerical hunting savitch in the second office automatically operated over said conductors responsive to the seizure of a trunk extending from the first ofiice to the second office for seizing a trunk extending from the second ofiice to the third ofiice in order to complete the connection.

In witness whereof, I hereunto subscribe my name this 2 11 day of October, A. Q.-1926.

FRITZ LUBBERGER. In witness reof, I hereunto subscribe my name this 28th day of October, A. D. 1926.

MAX LANGER. 

